Tyre for motor-vehicle wheels exhibiting a surface-worked annular strap at the sidewalls thereof

Abstract: The described tyre (1) is provided at the sidewalls (3) with an annular strap (8) within which a plurality of ribs (9) is formed, which ribs are disposed in mutual side by side relation and circumferentially distributed. The annular strap (8) is made in the form of a hollow on the respective sidewall (3) of the tyre (1) and is designed to receive informative inscriptions (12) the characters of which (13) are defined by projections (19) emerging from the surface of the annular strap itself.

Description: The present invention relates to a tyre for operating use on motor-vehicle wheels, of the type comprising: a pair of beads each of which is defined at an inner circumferential edge of the tyre; a pair of sidewalls, each of which is in the form of an annulus and extends in a radial direction and away from one of said beads; a tread band of substantially cylindrical conformation the opposite perimetric edges of which are joined to the sidewalls at respective buttress areas, said band exhibiting a surface-worked annular strap at the sidewalls. It is known that tyres presently used in the automotive field are externally provided with a tread band having the form of a cylindrical ring and arranged to rest on the roadway, two sidewalls extending in a radial direction from the opposite edges of the tread band and two beads defined at the end of the respective sidewalls along the inner circumferential edges of the tyre. In tyres hitherto depicted, the sidewalls have a substantially smooth surface on which different inscriptions such as brand of the tyre-producing company, model, particular technical data and other information, are printed. The above inscriptions sometimes encounter some readability problems in that the contrast between the inscription surface and background surface, that is the remaining surface of the tyre sidewall, is not very strong and in that the incident light on the tyre sidewall, apart from very favourable lighting conditions, creates two opposed circular sectors which are well-lighted but of very reduced width, whereas all the remaining portion of the sidewall is left in the shade, so that only a small part of said inscriptions is highlighted. As regards contrast, solutions tending to enhance it have been long since adopted, such as writing the inscriptions in relief with respect to the background, knurling the inscription surface or emphasizing the edges of said inscriptions with respect to the central part thereof. Therefore, these expedients have only partly solved the problem related to the inscription readability, and at all events without dealing with the aspect connected with the tyre sidewall lighting. It is yet to be noted that in the tyre vulcanization process carried out in a closed mould, it is required that the air that has been trapped between the mould cheek and the tyre sidewall should be vented during the mould closure: in order to enable this air escape, the solutions of the known art make it necessary to form a great number of small holes on the mould cheeks which holes not only require frequent and difficult mould cleaning operations, but also give rise to the presence, on the finished workpiece, of hair-like projections consisting of the vulcanization stems created by the elastomeric material penetrated into the small holes during the vulcanization step. These unaesthetic hair-like projections must be eliminated by carrying out a finish work on the vulcanized tyre. In addition to the above, a correct and optimal distribution of these small holes on the mould cheek for air escape purposes would inevitably involve the presence of some small holes on the inscriptions as well or in close proximity thereto: but since the relative hair-like projections would aesthetically impair these inscriptions to a great degree, it is better to form a greater number of small holes, provided that they are far from the inscriptions. From the US Ornamental Model DES. 87,418 a tyre for motor-vehicles has been known which has the sidewalls devoid of informative inscriptions and a rounded-profile tread. Two series of grooves depart from the tread centre line of said tyre and they symmetrically extend on the opposite sidewalls of the tyre until the bead area. In this tyre the problem related to the sidewall hair-like projections seems to be overcome by renouncing the inscriptions and through a plurality of grooves extending radially from the bead to the buttress and circumferentially distributed on the tyre sidewall, which grooves constitute the prolongation of the tread pattern grooves. Since these grooves ensure the air escape towards the thread, they make it useless to provide small venting holes on the mould cheeks. FR-A-2 661 871 discloses a tyre according to the preamble of claim 1 for motor-vehicle wheels formed with an annular decorative strap with converging ribs extending in such side strap. Should inscriptions be provided in the sidewall their surfaces would not be flat and such possible inscription would be positioned in portions of the sidewall that are devoid of ornaments, so that FR-A-2 661 871 does not show any inscription nor suggest any means for improving the readability of the inscriptions. In accordance with the present invention, the Applicant has found that by defining at the tyre sidewalls an annular strap exhibiting a plurality of circumferentially distributed ribs crossing the annular strap itself, it is possible to affix informative inscriptions on the surface of said strap the readability of which is greatly improved while at the same time achieving a better luminosity of the whole tyre sidewall and important advantages from the production point of view. The invention consists in a tyre as claimed in claim 1. In accordance with the invention, the annular strap is formed on the corresponding tyre sidewall in the form of a surface hollow of predetermined depth, said ribs having a height lower than said depth. Preferentially, the height of said ribs is not lower than half the depth of said surface hollow. According to a preferential choice, said informative inscriptions are defined by a plurality of projections emerging from said annular strap according to a height greater than that of said ribs and, preferably, greater than the depth of said surface hollow. In accordance with a further aspect of the invention, each of said ribs has a trapezium-shaped profile and a substantially rectilinear extension. In greater detail, each of said ribs extends from the inner perimetric edge to the outer perimetric edge according to a given angle of inclination with respect to a radial straight line issuing from the inner perimetric edge at the crossing point with the rib itself, each rib being spaced apart from the adjacent rib according to an arc that on the inner perimetric edge subtends a respective central angle of predetermined opening. In one embodiment said angle of inclination, identical for wall ribs, is generally included between 60° and 90° and, preferentially, lower than 85°. In said embodiment, the arc and the central angle are identical for all pairs of adjacent ribs. In particular the arc has an amplitude included between 0.8 mm and 5 mm whereas the central angle has an opening included between 0.0178° and 1.35°. According to a second embodiment of the tyre of the invention, a plurality of sectors of an annulus having the same angular extension is defined along the circumferential extension of said annular strap, each of them exhibiting, along the circumferential extension thereof, a gradual increase of the angle of inclination of the individual ribs, together with a gradual increase of the values of said arc and central angle. Preferably, the annular strap has two or four of said sectors of an annulus. In greater detail, in each of said sectors the value of said angle of inclination increases continuously from 0° to 90° while at the same time the value of said arc increases continuously from 0.8 mm to 5 mm and likewise the value of said central angle increases continuously from 0.0178° to 1.35°. According to a further embodiment of the invention, the annular strap has a predetermined number of sectors of an annulus having the same angular extension, preferably corresponding to 180°, each of said sectors exhibiting first and second series of ribs extending from the inner perimetric edge and the outer perimetric edge respectively, each rib of the first series intersecting a corresponding rib of the second series at a respective point of mutual break. In more detail, each rib of the first series is inclined in the opposite way to that of the corresponding rib of the second series with respect to a radial direction passing through the respective point of mutual break. Preferentially, said points of mutual break are consecutively aligned according to a spiral-shaped line extending from the inner perimetric edge to the outer perimetric edge. Finally, said ribs present in said annular strap are preferably in a number higher than 200. Further features and advantages will become more apparent from the detailed description of some preferred embodiments of a tyre for motor-vehicles exhibiting a surface-worked annular strap at the sidewalls, according to the present invention. This description is given hereinafter by way of non-limiting example with reference to the accompanying drawings, in which: Fig. 1 is a fragmentary perspective view, sectioned along a meridian plane, of a sidewall of a tyre provided with a surface-worked annular strap according to the present invention; Fig. 2 is a diagrammatic side view of one embodiment of the tyre in accordance with the invention; Figs. 3, 4 and 5 are diagrammatic side views of further embodiments of the tyre of the invention; Fig. 6 is an enlarged sectional view of a tyre sidewall taken along the line VI-VI in Fig. 2. Referring to the drawings, a motor-vehicle tyre exhibiting a surface-worked annular strap at the sidewalls in accordance with the present invention has been generally identified by reference numeral 1. In known manner, defined in the tyre 1 is a tread band 2 of substantially cylindrical conformation as well as two sidewalls 3 (only one of which is shown) in the form of an annulus extending in a substantially radial direction from the opposite edges of the tread band 2 towards the tyre axis. Each of said sidewalls 3 exhibits at the end a corresponding bead 4 defined along the inner circumferential edge of the tyre 1. At the beads 4 the tyre 1 is engaged on a rim (not shown) for defining a vehicle wheel. At each of the beads 4, the tyre 1 has a corresponding anchoring ring 5 adapted to locally stiffen the area at which the tyre is engaged to the rim and around which the opposite edges of one or more carcass plies 6 are wrapped, which plies extend over the whole section of the tyre. If the tyre 1 is of the radial type it is also provided with a circumferentially inextensible belt 7 disposed between the tread band 2 and carcass plies 6. As regards the tread band, it is provided, as known, with a raised pattern exhibiting ridges and/or plugs bounded by grooves and involving lamellae variously combined with each other so as to ensure the necessary behavioural qualities to the tyre in use, in particular road grip and resistance to the acquaplane. It is pointed out that by "tyre for operating use on motor-vehicle wheels" it is intended a new or remolded tyre in which the grooves of said raised pattern have a depth not lower than 2 mm which is the minimum value permissible by law and considered capable of ensuring a sufficient level of performance. In accordance with the present invention, an annular strap 8 is advantageously defined on the outer surface of at least one of the tyre sidewalls 3, on which strap a plurality of ribs 9 is formed, preferably more than 200 ribs disposed consecutively in side by side relation and circumferentially distributed. In greater detail, this annular strap has a radial extension delimited between an outer perimetric edge 11 substantially coincident with the perimetric edge of the tread band 2 at the buttress area 3a of the sidewall 3, and an inner perimetric edge 10 positioned within the area included between the circumferential line of maximum chord of the tyre and the corresponding bead: preferentially, this edge coincides with the centering stringcourse 20 located close to the bead 4 and delimiting the contact area between the tyre bead and the mounting rim with a safety zone. In other words, referring particularly to Fig. 6, being identified by "S" the section height of the tyre measured at the meridian plane m-m starting from the reference line "f" at the beads, the outer perimetric edge 11 of said tread band is in the radially external center line of the tyre sidewall, at a height "s 1 " of a value usually corresponding to 70% of S or even more, whereas the inner perimetric edge 10 is in the radially internal center line of the tyre sidewall, at an area included between the circumferential line of maximum chord of the tyre represented by the intersection point C between said line and the plane of the right section of the tyre (which point is at a height "s 2 " usually included between 40% and 60% of "S"), and the bead itself (line "f"). Preferably, the height "s 3 " of the inner perimetric edge 10 will be included between 10% and 35% of "S" and more preferably will coincide with the height "s" of said centering stringcourse. By way of example only, in a prototype tyre size 175/70 R 13 where S corresponds to 126 mm, s 1 , s 2 and s 3 measure 94 mm (74%), 60 mm (48%) and 38 mm (30%), respectively. Each of the ribs 9 has a wedge-shaped or trapezium-shaped (of easier manufacture) profile seen in right section, and extends substantially rectilinearly in a direction intersecting the outer perimetric edge 11 and can also intersect the inner perimetric edge 10 of said annular strap 8. It is pointed out that the presence of ribs 9 in the annular strap 8 defines a surface reflecting the incident light on the tyre sidewall 3 according to a reflection arc of greatly wider amplitude than in the case of a smooth surface. This quality is advantageously utilized for optimizing the readability of informative inscriptions 12 put on the tyre sidewall. In fact, in accordance with the present invention, these informative inscriptions 12 are made by characters 13 printed at the annular strap 8 in a unitary manner during the vulcanization of the tyre 1, using the same elastomeric material forming the sidewall 3. These characters having smooth surfaces 13a are optically differentiated from the surface defined by the ribs 9, by effect of the different reflection of the incident light. Therefore the readability of the informative inscriptions 12 printed on the annular strap 8 is greatly improved as compared to the readability of the same inscriptions printed, in accordance with the traditional known art, on a smooth-surface sidewall or a smooth area of the sidewall itself. In order to optimize the effect described above in short, the applicant has developed several preferential embodiments to be described in detail hereinafter, in which the ribs 9 are disposed within the annular strap according to different distribution modalities. In greater detail, referring to Figs. 2, 3 and 4, the annular strap 8 has ribs 9 extending from the inner perimetric edge 10 to the outer perimetric edge 11. Each of these ribs defines a predetermined angle of inclination "α" with respect to a radial straight line "n" issuing from the inner perimetric edge 10 at the intersecting point between this inner perimetric edge and the rib itself. In addition, each rib 9 defines with the adjacent rib, an arc "l" of predetermined length on the inner perimetric edge 10. This arc "l" then subtends a corresponding central angle denoted "β" in the accompanying drawings. In greater detail, in the embodiment shown in Fig. 2, the angle of inclination "α" in particular generally takes a value included between 60° and 90° and preferably not higher than 85°. In the same embodiment the arc "l" and consequently the corresponding central angle "β" are identical for all pairs of adjacent ribs 9. According to a preferential choice, the arc "l" has a value ranging between 0.8 mm and 5 mm. As regards the central angle "β", the opening thereof is preferentially included between 0.0178° and 1.350°. It will be clear that the values of arc "l" and angle "β" establish the density of said ribs on the tyre sidewall. In the embodiments shown in Figs. 3 and 4, it is provided that the annular strap 8 be divided into a plurality of sectors of an annulus of the same angular amplitude. In particular, Fig. 3 shows a tyre 1 the annular strap 8 of which has two sectors of an annulus 14, whereas Fig. 4 shows a tyre 1 the annular strap 8 of which is divided into four sectors 14. Along the circumferential extension of each of said sectors, the angle of inclination "α" of said ribs 9 has a gradually increasing value and correspondingly a gradual increase of the arc "l" and the respective central angle "β" occurs. More particularly, referring to the accompanying figures, travelling over each of said sectors 14 of the annular strap 8 in a counterclockwise direction, it is noticed that the angle of inclination "α" rises from a start value preferably equal to 0° to which a rib 9 oriented in a substantially radial direction corresponds, to a final value preferably equal to 90°, to which a rib directed tangentially to the inner perimetric edge 10 corresponds. In each of said sectors 14 as the angle of inclination "α" gradually increases from 0° to 90°, a gradual increasing of the arc "l" occurs from a start value equal to 0.8 mm to a final value equal to 5 mm, as well as a gradual increase of the central angle "β" from a start value of 0.0178° to a final value of 1.350°. The above has the purpose of avoiding the increases or reductions in density between contiguous ribs which would arise by effect of the variation of inclination in the ribs while keeping the value of the central angle "β" constant. It is apparent from Figs. 3 and 4 that in each sector 14 there is an interference area between the substantially radial ribs to be formed at the beginning of the sector and those substantially tangent to the inner perimetric edge coming from the contiguous sector. The preferential solution for these areas is the one shown in said Figs. 3 and 4, consisting in leaving the tangential ribs while eliminating the radial ones, so that (Fig. 4) the first rib 21, completely extended between the two perimetric edges, is inclined to the diameter passing by the end of sector 14 according to an angle "δ" of a value not lower than 60°. According to a further preferential embodiment shown in Fig. 5, each of the two sectors 14 into which the annular strap 8 is divided exhibits a first series 15 and a second series 16 of ribs 9 extending from the inner perimetric edge 10 and the outer perimetric edge 11 of the annular strap 8, respectively. Preferentially, each rib 9 of the first series 15 intersects a corresponding rib 9 of the second series 16 defining a respective point of mutual break 17. In accordance with the preferential embodiment shown, each rib 9 of the first series 15 is inclined in the opposite direction to the corresponding rib 9 of the second series 16 with respect to a radial direction "r" passing by the respective point of mutual break 17 of the two ribs 9. In addition, the points of mutual break 17 of the different ribs 9 of each sector 14 are aligned according to a spiral-shaped line extending from the inner perimetric edge 10 to the outer perimetric edge 11 of the annular strap 8. From the foregoing explanation several other embodiments of said annular strap can be easily drawn which are not herein show. There are for example at least two further versions according to which: (a) the annular strap 8 is provided with two series of opposite ribs forming on said strap a knurling consisting of the intersecting ribs, and (b) the annular strap 8 is divided into two coaxial circular portions each provided with its own rib type according to the versions previously depicted. In accordance with a further aspect of the present invention, the annular strap 8 on which said ribs 9 extend is formed on the corresponding tyre sidewall in the form of a surface hollow of predetermined depth "p" as shown in Fig. 6. In an original manner, the ribs 9 axially projecting from the annular strap 8 have a height "h" lower that the depth "p" of said surface hollow. However, the height "h" of the ribs 9 is not lower than half the depth "p" of said surface hollow. In a new manner and in accordance with the present invention, any informative inscriptions 12 reproduced at the annular strap 8 are defined by a plurality of projections 19 emerging from said annular strap 8 according to a height "H" greater than the height "h" of the ribs and preferentially greater than the depth "p" of the surface hollow. Still by way of example, in the previously cited tyre the depth "p" of the surface hollow is 0.45 mm, the rib height "h" is 0.35 mm and the height "H" of projections 19 is 0.80 mm. The invention achieves important advantages. Firstly, the rib assembly reflects the incident light on the sidewall thereby creating a diffuse luminosity in two diametrically opposite circular sectors of important width so as to make the various inscriptions present therein much more readable (the readability being exclusively due to the above reason), including those inscriptions that have been printed on the sidewall surface portion externally of said annular strap. Secondly, as it has been already pointed out, the annular strap 8 provided with ribs 9 defines a surface particularly adapted to receive inscriptions 12 or information signs, In fact, the characters 13 of the inscriptions 12 exhibit a substantially smooth outer surface 13a reflecting the incident light beams in a different manner than the surface of the annular strap 8 provided with ribs 9, with a very marked contrast effect. Consequently, the character surface 13a has a substantially differentiated luminosity, that is a discontinuity in the light tone with respect to the surface of the annular strap 8. This discontinuity greatly improves the degree of readability of the informative inscriptions 12 under any read angle. The above described effect is also emphasized by the fact that the ribs 9 and projections 19 defining the individual characters 13 of the inscriptions 12 axially project from the annular strap 8 according to mutually differentiated heights "h" and "H". As to the arrangement of said inscriptions, they can be disposed according to a rectilinear configuration, not shown, optionally parallel to a rib and lie on the rib itself, or be oriented according to a direction inclined to all ribs present in the inscription area. The inscriptions may also be disposed, in accordance with the traditional art shown, so as to form an arc of a circumference coaxial with the tyre sidewall. It is also to be pointed out that the presence on the sidewall 3 of an annular strap provided with ribs 9 in accordance with the present invention involves an important simplification in the tyre manufacture, referring particularly to the tyre vulcanization step carried out in a corresponding mould. In fact, these ribs define a plurality of venting channels disposed mutually in side by side relation and homogeneously distributed on the mould surface which are capable of radially conveying the air trapped between the tyre sidewall and the mould cheek towards the bead 4 and buttress 3a areas, where said air can be easily discharged due to the approaching between the different metal parts of the mould. Therefore, by virtue of the present invention the usual discharge holes present on the mould cheeks can be eliminated thereby avoiding the formation of vulcanization stems. As a result, the already mentioned finish operation of the vulcanized tyre sidewalls is not required any longer. Obviously a person skilled in the art will conceive many modifications and variations without departing from the scope of the present invention as defined in the appended claims.

Claims: A tyre for operating use on motor-vehicle wheels, comprising: a pair of beads (4) each of which is defined at an inner circumferential edge of the tyre (1); a pair of sidewalls (3), each of which is in the form of an annulus and extends in a radial direction away from one of said beads (4); a tread band (2) of substantially cylindrical conformation the opposite perimetric edges of which are joined to the sidewalls (3) at respective buttress areas (3a), said band exhibiting a surface-worked annular portion at the sidewalls, on the outer surface of at least one of said sidewalls (3) being defined an annular strap (8) the radial extension of which is delimited between an inner perimetric edge (10) disposed in the area included between the relative bead (4) and the maximum-chord circumferential line of the tyre, and an outer perimetric edge (11) substantially coincident with the perimetric edge of the tread band (2) at the corresponding buttress area, on said annular strap (8) a plurality of substantially rectilinear ribs (9) being formed which are disposed consecutively in side by side relation, are circumferentially distributed and extend each substantially according to a direction intersecting at least the outer perimetric edge (11) of said annular strap (8), with informative inscriptions (12) being formed on said annular strap (8), characterized in that said inscriptions (12) are formed as a solid characters on the annular strap (8) and are defined by a plurality of projections (19) having smooth surfaces (13a), emerging from said annular strap according to a height ("H") greater then the height ("h") of said ribs (9). A tyre according to claim 1, characterized in that said annular strap (8) is formed on the corresponding tyre sidewall (3) in the form of a surface hollow of predetermined depth ("p"). A tyre according to claim 2, characterized in that said ribs (9) have a height ("h") lower than the depth ("p") of said surface hollow. A tyre according to claim 3, characterized in that said ribs (9) have a height ("h") not lower than half the depth ("p") of said surface hollow. A tyre according to claims 1 to 4, characterized in that said annular strap (8) is clear of residual vulcanization stems. A tyre according to claim 1, characterized in that said ribs (9) have a trapezium-shaped profile in cross-section. A tyre according to claim 1, characterized in that each of said ribs (9) extends from the inner perimetric edge (10) to the outer perimetric edge 11 according to a given angle of inclination α with respect to a radial straight line ("n") issuing from the inner perimetric edge (10) at the crossing point with the rib itself, each rib (9) being spaced apart from the adjacent rib according to an arc ("l") that on said inner perimetric edge (10) subtends a respective central angle β of predetermined opening. A tyre according to claim 7, characterized in that said angle of inclination α is identical for all ribs 9. A tyre according to claim 8, characterized in that said angle of inclination ( α ) is included between 60° and 90°. A tyre according to claim 9, characterized in that said angle of inclination α is lower than 85°. A tyre according to claim 7, characterized in that said arc "l" and central angle β are identical for all pairs of adjacent ribs 9. A tyre according to claim 11, characterized in that said arc ("l") is comprised between 0.8 mm and 5 mm. A tyre according to claim 11, characterized in that said central angle ( β ) has an opening included between 0.0178° and 1.35°. A tyre according to claim 7, characterized in that a plurality of sectors of an annulus (14) having the same angular extension is defined along the circumferential extension of said annular strap (8), each of them exhibiting, along the circumferential extension thereof, a gradual increase of the angle of inclination ( α ) of the individual ribs (9), together with a corresponding gradual increase of the values of said arc "l" and central angle β . A tyre according to claim 14, characterized in that the value of said angle of inclination ( α ) continuously increases from 0° to 90° in each of said sectors (14). A tyre according to claim 15, characterized in that the value of said arc ("l") increases continuously from 0.8 mm to 5 mm in each of said sectors (14). A tyre according to claim 15, characterized in that the value of said central angle ( β ) increases continuously from 0.0178° to 1.35° in each of said sectors (14). A tyre according to claim 15, characterized in that the annular strap (8) has two of said sectors of an annulus (14). A tyre according to claim 15, characterized in that the annular strap (8) has four of said sectors of an annulus (14). A tyre according to claim 6, characterized in that the annular strap (8) has a predetermined number of sectors of an annulus (14) of the same angular extension, each of said sectors exhibiting first (15) and second (16) series of ribs (9) extending from the inner perimetric edge (10) and outer perimetric edge (11) respectively, each rib (9) of the first series intersecting a corresponding rib (9) of the second series (16) at a respective point of mutual break (17). A tyre according to claim 20, characterized in that each rib (9) of the first series (15) is inclined in the opposite direction to that of the corresponding rib (9) of the second series (16) with respect to a radial direction ("r") passing through the respective point of mutual break (17). A tyre according to claim 20, characterized in that the annular strap (8) is divided into two sectors (14) of an angular extension substantially equal to 180°. A tyre according to claim 20, characterized in that said points of mutual break (17) are consecutively aligned according to a spiral-shaped line extending from the inner perimetric edge (10) to the outer perimetric edge (11). A tyre according to claim 1, characterized in that said ribs (9) present on said annular strap (8) are in a number higher than 200. A tyre according to claim 1, characterized in that at least one of said inscriptions is disposed according to a straight line. A tyre according to claim 25, characterized in that at least one of said inscriptions lies along one of said ribs. A tyre according to claim 1, characterized in that said annular strap (8) is divided into two coaxial annular portions, each provided with a plurality of ribs of its own.

Inventors: BARRESE ANTONIO, BATTAINI MASSIMO, BARRESE, ANTONIO, BATTAINI, MASSIMO
Applicants: PIRELLI, PIRELLI COORDINAMENTO PNEUMATICI S.P.A.
Application year: 1994
Main classification: B60C13
IPC codes: B60C13